Bare dye or wafer level packages include a redistribution layer (RDL) for Touting signals from the internal circuitry of an integrated circuit to external solder balls. The redistribution layer must be protected against oxidation and corrosion to ensure the integrity of the integrated circuit. Typically, the redistribution layer is protected from oxidation and corrosion using expensive special process flows.
For example, one type of wafer level package includes special metal stacks, such as Cu, Ni, and Au to protect the redistribution layer from oxidation and corrosion. The special metal stacks require large throughput, however, and the final layer of the metal stack needs to be a noble metal. Additional materials such as a solder stop material layer deposited on top of the noble material, however, do not adhere well to the noble material.
Other types of wafer level packages use special geometrics to avoid oxidation and corrosion of the redistribution layer. Geometrical adaptations can be realized by separation of the redistribution layer and under bump metallization (UBM). The use of special geometries requires additional photolithography steps and therefore increases the cost.
For these and other reasons, there is a need for the present invention.